There is different configuration that you should take in consideration between CAN and CANFD.
For example, for datafieldSize any size bigger than 8 is for CANFD.
You can see this as a note in the SDK

Also, default configuration taken from the instruction MCAN_GetDefaultConfig from the SDK, CANFD is not activated by default.
You can take as reference the SDK example mcan_interrupt _transfer, even though it doesn't use two CAN configuration at the same time it shows how to use them separately.